To make a belt so as to be removed without extracting a shaft from a pulley by forming a movable side bearing with a bearing body, a slip-stop piece, an adjuster and a groove installed in this adjuster, and also forming an adjusting means with a bolt, a set nut and a clamp nut, respectively.

When a belt is removed, first of all, a clamp nut 43 is loosened to some extent, making a bolt 39 into a state of being rotatable, and then this bolt 39 is rotated and it is taken out of a groove 31 of an adjuster 29 in a movable side bearing 33, whereby this bearing 33 is made into a state of freedom in a long hole 7. Next, a driven pulley 11 is shifted to some extent and, after loosening the extent of tension of the belt to the full, the movable bearing 33 is removed away and thus the belt is made to be removable without extracting a shaft 35 from the driven pulley 11.